Oh It Happens Sometimes Go To Settings Then More Then Mobile Network Then Activate Data Connection ( The Solution Of This Problem Is Just Turn The Data Connection At Settings ) I Hope It Works...
Go To Phone/Call Then Call *#*#4636#*#* Then Click Phone Information Then Scroll Down And Click Your Network Then Click GSM Only So Your Signal May Increased Signal. I Hope It Works
It Because Of Ram Overloading Or Memory Full So You Need To Uninstall Some Apps And Clear Some Files I Recommend You To Use Clean Master Or Ccleaner Apk. I Hope It Works